The invention relates generally to a fiberoptic multi-parameter sensing system and method for monitoring a turbomachinery system operation status, and more particularly to a system and method capable of providing simultaneously static and dynamic torque and vibration sensing from a turbomachinery system.
The measurement of the turbomachinery torques that varies along its shafts provides key information for design engineers to validate and improve the system efficiency. Also, mechanical misalignment, the rubbing motion between rotor and stator, distortion of shafts, slippage of couplings, and other random forces are normally causes for rotors and shafts suffering from static and dynamic torques, and flexural and torsional vibration that lead to most of fault events. Torques and vibrations are some of the critical parameters that may be measured to monitor power generation efficiency or degradation in a turbomachinery system, which may comprise a steam turbine, generator, load gear, and gas turbine. They can be measured by resistive strain gages, stationary proximity, magnetostrictive, and magnetoelastic sensors. These rotary based sensors must be mounted onto or in proximity to the rotor and shaft surface, which may not always be possible because of the space limitations. The operation of these conventional measurement technologies unfortunately suffers from the variation of the environmental conditions such as temperature, pressure, clearance, moisture, and electromagnetic interference. Since a typical turbomachinery system operates at temperatures from about 100° F. to about 1200° F., and under high humidity, it is exposed to varied torsional or flexural vibrations, and radial thermal expansion conditions due to large dynamic mechanical deformation and flexural and torsional vibrations. They all affect the accuracy and life of these sensing devices. Such sensing devices are therefore not reliable for long-term operation in large turbomachinery.
Rotor and shaft torque sensing include determining the amount of power a turbine, or other rotating device, generates or consumes. In the industrial world, ISO 9000 and other quality control specifications are now requested to measure torque during manufacturing, especially when fasteners are applied. There presently exists no practical sensing system that can measure both static and dynamic torque of a turbomachinery system, such as steam turbine rotor and shaft surface whenever the sensing location requires that sensing occurs under harsh conditions.
Known optical-based torque sensing techniques employ free-space-based laser beam deflection methods to measure torque by reflecting a laser beam from a micro-mirror that is embedded onto a shaft surface. Such devices are difficult to interface in a steam turbine environment due to the absorption of the laser beam by the steam, and also due to the optical surface maintenance requirements of the micro-mirror which is sensitive to the steam flow environment as well as the mechanical alignment and vibration.
Similar optical interference-based vibration measurement systems are known for measuring mechanical deformation and displacement but these systems are not designed for a turbomachinery system to provide steam turbine rotor shaft mechanical deformation associated with vibration detection because the thermal induced expansion makes it difficult to maintain optical focus and signal integrity in a dynamic environment.
All of the current technologies such as stationary proximity, resistive strain gages, magnetostrictive and magnetoelastic sensors, are not robust enough to survive in a turbomachinery system, such as a steam turbine environment, for the life of the machine, and all are temperature sensitive. Such a thermal-sensitive property has caused serious reliability issues and are the cause of inaccuracies.
Another problematic issue related to current technologies is directed to the installation parameters of these conventional torque/vibration-sensing devices in the turbomachinery system, such as steam turbine environment, including without limitation, moisture, pressure, fluctuated electromagnetic field interference, temperatures of 100° F.-1200° F., and rotor flexural or torsional vibration. A strain gage, for example, needs to be mounted on the rotor surface, and a magnetostrictive sensor needs to be mounted close to the shaft surface with a gap or clearance less than a few hundred micrometers. Temperature fluctuations in a turbomachinery system, such as different stages of a steam turbine, induce significant transient rotor thermal expansion and flexural or torsional vibration. In a harsh environment, reliable torque and vibration measurements among steam turbine-generator, generator-load gear, and load gear-gas turbine sections and among individual steam turbine stages will allow performance to be monitored and maintenance outages to be more optimally scheduled, maximizing turbine availability and output.
Further, flexural and torsional vibrations caused by shifts of load in the steam turbine-generator, generator-load gear, and load gear-gas turbine can produce transient oscillations that exceed steady state stress levels under full load conditions. Such transient nonlinear vibrational events can induce bearing wearing, bending deformation of shafts and high torque loading, and threatens the stability of a steam turbine power generation system, among other effects. Conventional vibration sensing technology such as accelerometers, strain gages, proximity probes and tachometers may be limited either by steam turbine harsh environment conditions including without limitation, temperature, pressure, steam, dust particles, moisture and high flow rate, or by their nature as contact and electrical sensing devices.
Under normal shaft operating conditions that correspond to stable equilibrium status, the observed low-frequency random vibration signal although small, could be the result of the rubbing motion between rotor and stator, distortion of shafts, slippage of couplings and other random forces. Flexural vibration modes are caused mainly from a rotating system mechanical misalignment, temperature distribution and unbalance; while the torsional vibration may be due to shaft loading condition variation-induced torque dynamics and transient rotating speed variations. External unknown excitation forces, transient power switching and unstable global system operation can also induce transient nonlinear vibration modes that could have high vibration amplitudes. In addition, deterioration of the turbine blades will reduce output and can be monitored via a reduction in torque and vibration frequency variations.
In view of the above, it would be both advantageous and beneficial to provide a practical solution for an online turbomachinery system, such as a steam turbine, torque and vibration analysis for improving power generation performance as well as power generation efficiency control and optimization. This solution should provide a reliable means of measuring static and dynamic torque, linear and nonlinear vibrations from rotating shafts or a reliable means of fault event diagnostics and prognostics. Reliable torque and vibration measurements between turbine sections and between individual turbine stages in a turbomachinery system will allow performance to be monitored and maintenance outages to be more optimally scheduled, maximizing turbomachinery system power generation efficiency. It would be further advantageous if the system and method of static and dynamic torque sensing for a turbomachinery system could be easily adapted to also reliably measure linear and non-linear shaft vibration characteristics.